1. Field of the Invention
The present invention relates to a valve timing adjusting apparatus for controlling valve timing of a valve that is opened and closed by a camshaft through torque transmitted from a crankshaft of an internal combustion engine.
2. Description of Related Art
A conventional hydraulic valve timing adjusting apparatus is known to include a housing and a vane rotor and to adjust valve timing using hydraulic oil supplied from a supply source, such as a pump. The housing is rotatable synchronously with a crankshaft of an internal combustion engine, and the vane rotor is rotatable synchronously with a camshaft of the internal combustion engine. In general, in the hydraulic valve timing adjusting apparatus, the vane rotor has a vane that defines inside the housing into an advance fluid chamber and a retard fluid chamber that are arranged in a circumferential direction. The introduction of hydraulic oil from the supply source into the advance fluid chamber or the retard fluid chamber changes a rotational phase of the vane rotor relative to the housing correspondingly in an advance direction or a retard direction in order to adjust the valve timing.
JP-A-2002-357105 corresponding to US20020139332 shows a hydraulic valve timing adjusting apparatus that regulates a change of the rotational phase within a range or a region between a full advance phase and a full retard phase. More specifically, in the apparatus of JP-A-2002-357105, before stopping of the internal combustion engine, a pin supported by the vane rotor is fitted with the vane rotor. As a result, the rotational phase is regulated to be changeable within a start phase region that allows the internal combustion engine to start, and the above state of the rotational phase regulated in the start phase region remains the same until the starting of the internal combustion engine in the next operation. Thus, startability of the internal combustion engine or engine startability is substantially achieved.
In the apparatus of JP-A-2002-357105, the internal combustion engine may stop instantly due to the occurrence of abnormality, the internal combustion engine may be locked before the pin regulates the rotational phase within the start phase region. In the above state, cranking of the internal combustion engine starts in a state, where the rotational phase is set out of the start phase region, and thereby the engine startability may deteriorate disadvantageously.
Thus, the inventors have studied a technique, in which the rotational phase, which is out of the start phase region, is changed to stay within the start phase region in order to achieve sufficient engine startability. Then, it is found that the engine startability is sufficiently achieved by introducing hydraulic oil into a specific fluid chamber at the time of starting of the internal combustion engine by cranking the engine. In the above, The specific fluid chamber corresponds to one of the advance and retard fluid chambers, and when hydraulic oil is introduced to the specific fluid chamber, the rotational phase is changed to stay within the start phase region.
However, in a low-temperature environment, where hydraulic oil has a high degree of viscosity, the inventors have found after the further study that the above technique may not achieve the desired engine startability disadvantageously. Then, after intense study, the inventors further found that in an apparatus, in which torque from the camshaft is applied to the vane rotor at the starting of the internal combustion engine, when force caused by the variation of the torque is applied to the vane rotor in a direction to change the rotational phase to the start phase region, the volume of the specific fluid chamber increases accordingly. Thus, in a case, where hydraulic oil has higher degree of viscosity, the introduction of the hydraulic oil into the specific fluid chamber may be delayed relative to the increase of the volume of the chamber, and thereby a negative pressure is prone to be generated in the specific fluid chamber. The generation of the negative pressure may deteriorate the rotation of the vane rotor relative to the housing, and thereby it may become difficult to change the rotational phase to the start phase region disadvantageously.